What? "Is he joking?" "Everyone knows the yellow tang, Zebrasoma flavescens is the most popular, hardiest member of the Doctorfish family." Well, the yellow is a tough customer if collected and housed correctly. But I assure you that it has nothing over the Sohal, Zebra, or Red Sea Clown Surgeon, Acanthurus sohal.
This fish has much going for it; good looks, ready food acceptance, disease resistance, active, interesting behavior. The only negative I would have applied to it in years past is "expense"; but no longer. Sohal tangs are Red Sea endemics, only found in that magical area; and their cost has come down with the recent growth in exports from the area.
Acanthurus sohal is still not cheap, but well worth the investment in terms of beauty and longevity.
Classification: Taxonomy, Relation With Other Groups
Surgeonfishes are part of a loose assemblage in the largest Order of fishes, the Perciformes, in the Sub-order Acanthuroidea. Related families include the Siganidae (Rabbitfishes like the Foxface, Lo vulpinis), scats (Scatophagidae), and Moorish Idol (family Zanclidae) among others. Think about the traits these families members have in common. Bodies that are deeply laterally compressed; small mouths; relatively large swim bladders; with elongate nasal bones that give a high-headed appearance. They all have a single dorsal fin with spines and soft rays; smallish gill openings; lunate caudal fins; 22 or 23 vertebrae.
The surgeonfish family, Acanthuridae and its seventy-two species should be familiar to you; several members are used for marine aquariums and food fishes. Also called, Doctorfish, and Tangs these bony fishes are distinguished by their elaborate spine-locking mechanism (a recessed groove for the first dorsal and anal fin support), and the knife-like projections (Acanthus is Greek for "thorn") they bear on their caudal peduncles.
All tangs are principally herbivorous, feeding mostly on algae. Another salient characteristic is their passing through a bizarre transparent larval stage termed the acronurus stage.
There are six genera of surgeons; Naso, Paracanthurus, Prionurus, Zebrasoma, Ctenochaetus and Acanthurus. Some other members of the genus Acanthurus ("Ah-Kan-Thur-Us") you've probably seen:
Acanthurus achilles (Achilles tang)
Acanthurus coeruleus (the Atlantic blue tang)
Acanthurus glaucopareius (Powder brown or gold-rimmed surgeon)
Acanthurus japonicus (Gold-rimmed surgeon)
Acanthurus leucosternon (Powder blue tang)
Acanthurus lineatus (Clown surgeon)
Acanthurus olivaceus (Orange shoulder tang)
Acanthurus triostegus (Convict tang)
Surgeons are entirely marine. They are found in all tropical seas, mostly as pelagic reef fishes, though some are oceanic. Acanthurus sohal is confined to the Red Sea.
Though some open-ocean surgeons approach two feet in length, the Sohal generally max's out at about eight inches in captivity.
Selection: General to Specific
I generally urge folks to consider four criteria separately and together when judging the acquisition of acanthurids: body conformation, color, behavior, and time in captivity. For the sohal tang, this is almost always superfluous. I have rarely seen a defective imported specimen.
Depending on how long your dealer has had the sohal in their care it might have "thinned" out. If not too pinched in and still eating (ask for a demonstration); the fish should revive and quickly fill out.
Of course you should be on the look out for usual disqualifiers; cuts, sores, obvious poor care... but outside these human-caused problems, this species is exceptionally tough and consistently of high initial quality.
Sohals live close to reefs and the open edge of same. They appreciate broken physical environments with rock, coral skeletons to pick over, and plenty of open space to swim about. Like the other members of its genus, this Acanthurus is a fast moving, active swimmer that needs room to move.
As with other Red Sea livestock, sohal tangs need consistent, high quality water. The salinity should be kept near 1.025 and constant; pH should be buffered between 8.2 and 8.4., and temperature in the mid seventies to low eighties degrees Fahrenheit.
Sohals are big-eaters and defecators; their system should be vigorously circulated, aerated and filtered. Do you think a redundant power-head, outside water pump, bubbler would be a good idea? Me too.
Some tang species are prime candidates for a degenerative condition called "head and lateral line erosion" (HLLE), a pitting of the pores of the lateralis system. Various theories point to stray voltage, nutritional deficiencies, bacterial, Protozoal involvement... and "water quality" as root causes alone, or in concert. Whatever the sources, for the latter concern, a maximum measurable nitrate level of 25ppm kept in line via filtration and water changes is suggested.
As with most members of its genus, the Sohal is best kept "celibitaire", one to a tank. Acanthurus tangs can get into nasty scruffs with other fishes, but "to the death" ones with conspecifics and ones that look too much like their own.
As for placing sohal tangs in "reef" systems, I've seen them used as such, and read of others experiences through the electronic bulletin boards. This species, when gotten small (3-4") typically leaves invertebrates alone and is useful for algae control.
Unless you have a system of hundreds of gallons you should stick with one Sohal. Other species in the genus Acanthurus should be avoided or chosen and introduced with extreme care. Pay special attention to introducing fishes of decidedly different size and place the smaller individuals first. Other less dominant fishes in the system should be afforded as much hiding space and crevices as possible.
Sohals, like all tangs, tend to get damaged, even tossed out on to the floor during handling. Try to avoid netting them altogether by directing specimens into open doubled-bags or specimen containers underwater. Watch your hands at all times around Surgeonfishes; their fin spines and "thorns" are painfully sharp, and they know how to use them; against tankmates, and humans.
I have yet to see or hear of a sohal tang attacked by a tankmate, or challenged on the reef by other than other Acanthurus; and then only till one retreated.
Reproduction, Sexual Differentiation:
Not successfully spawned and reared in captivity as yet. There are no definitive color or structural differences between the sexes. The Sohal probably spawns as other tangs, congregating in pairs tied to lunar cycles, releasing floating gametes to their surface fates.
Sohal tangs are perhaps the most omnivorous of Surgeonfishes. They do need their daily greens, but accept greedily all other forms of foods, meaty and non.
Please do not rely solely on terrestrial lettuces for your tangs green-needs. Oriental store algae, live rock and algal sources, specialty flakes and more are better sources of nutrition.
Food should be offered often in small amounts; ideally through the use of an automatic feeder, stocked with an appropriate mix of prepared foods, set to a maximum number of feedings. When awake, surgeons are constantly on the prowl for edibles.
Disease: Infectious, Parasitic, Nutritional, Genetic, Social
Some other writers have marked Acanthurus sohal as being particularly susceptible to marine ich (Cryptocaryoniasis); I have not found this to be the case. Such instances of Protozoal or bacterial infection should be dealt with by avoidance; quarantine and dipping. A word of caution re tangs; constant treatment with captive "remedies" like copper has proven to be counterproductive; as essential gut-fauna are attacked as well.
Don't be dissuaded (out of hand) by the price of Red Sea specimens for your marine system. Most are well worth the extra cost. The Sohal tang is one prime example. Almost all imported specimens thrive; and they're gorgeous. The best of their family? You must decide for yourself.
Campbell, Douglas G. 1979. Fishes for the beginner, A guide for the new marine hobbyist, Parts three and four, Tangs. FAMA 1,2/79
Colin, P.L.; Clavijo I.E. 1988. Spawning activity of fishes producing pelagic eggs on a shelf edge coral reef, southwestern Puerto Rico. Bull. Mar. Sci. vol. 43, no. 2, pp. 249-279.
Debelius, H. 1975? Useful information on surgeon fish. Aquarium digest Intl. #29, pp 31-33., #31, pp 28-29.
Fenner, Robert. 1996. Will the real powder brown tang please swim up? TFH 3/96.
Fenner, Robert. 1998. The Conscientious Marine Aquarist. Microcosm, VT. 432pp.
Fishelson, L., Montgomery, W.L., Myrberg, A.A. 1985. A unique symbiosis in the gut of tropical herbivorous surgeonfishes (Acanthuridae: Teleostei) from the Red Sea. Science (Wash.) vol. 229, no. 4708, pp. 49-51; 1985.
Jones, Lawrence L.C. 1988. Care and maintenance of tangs in captivity. Part one: Food and feeding. FAMA 10/88.
Maisey, John G. 1996. Fossil surgeonfishes. TFH 4/96.
Nelson, Joseph S. 1984. Fishes of the World. 2nd Ed. Wiley.
Sands, David. 1994. Superb surgeons. FAMA 10/94.